"Microsoft's Surface Pro tablet, due on February 9th, will have a smaller amount of storage space than expected. A company spokesperson has confirmed to The Verge that the 64GB edition of Surface Pro will have 23GB of free storage out of the box. The 128GB model will have 83GB of free storage. It appears that the Windows 8 install, built-in apps, and a recovery partition will make up the 41GB total on the base Surface Pro model." Oh Microsoft.

$ gb used as opposed to 41 gb. For your example, that breaks down to:
32 gb iPhone: 12.5% of space used, btw a good chunk of that is simply filesystem overhead and other formatting, not to mention the 1024 vs 1000 byte marketing tactic.
Surface Pro: 64% of the disk space used and, while roughly the same amount as the iPhone goes to filesystem overhead not to mention the same marketing tactics as above, that's certainly not true for the rest of the used space. This is false marketing, pure and simple because, at the $899 entry price, no one would ever buy a tablet marketed as having 23 gb of useable space. That would expose it as the rip-off that it is.